It is found that the volume efficiency of the prior art cylinder cannot be enhanced on account of insufficient intake air. Although it is proposed to open the valve earlier and delay the close thereof or use a turbo-charger to obviate the drawback, the function will still be limited and the cylinder cannot provide higher volume efficiency as the piston moves quickly and the time for intaking air is shortened.
Therefore, it is an object of the present invention to provide a cylinder which may obviate and mitigate the above-mentioned drawbacks.